1. Field of the Invention
The present invention relates to light guides, more particularly to a light guide for use in an image reading apparatus.
2. Description of Related Art
For example, a light source device 500 shown in FIG. 8 is a known light source device including a conventional light guide. FIG. 8 is a cross-sectional structure diagram of the light source device 500 including a conventional light guide 502.
The light source device 500 includes the light guide 502, a light source 504, and a reflective member 506, as shown in FIG. 8. The light guide 502 is made of transparent resin, and extends in a left-right direction in FIG. 8. The light guide 502 has a prism that reflects light upwardly inside the light guide 502, formed on its bottom surface. The light source 504 is directed to the left end of the light guide 502. Moreover, the reflective member 506 surrounds the gap between the light guide 502 and the light source 504.
In the light source device 500 thus configured, light emitted by the light source 504 enters the light guide 502 from the left end. At this time, light that propagates from the gap between the light guide 502 and the light source 504 toward the outside of the light source device 500 is reflected by the reflective member 506, and enters the light guide 502 from the left end. The light having entered the light guide 502 travels rightward while repeatedly experiencing total reflection within the light guide 502, and then the light is reflected upwardly by the prism formed in the light guide 502. Since the light source device 500 is provided with the reflective member 506, light is inhibited from leaking out of the light source device 500 through the gap between the light guide 502 and the light source 504.
Incidentally, the light source device 500 uses the reflective member 506 to inhibit leakage of light. When reflecting light, the reflective member 506 absorbs part of the light. Therefore, the light source device 500 cannot efficiently utilize light emitted by the light source 504.
Note that, for example, illumination optics described in Japanese Patent Laid-Open Publication No. 2005-123675 are a known invention related to a conventional light guide. The illumination optics confine light inside a light guiding means through total reflection without using a reflective member. However, in the illumination optics described in Japanese Patent Laid-Open Publication No. 2005-123675, light does not enter the light guiding means from an end in a longitudinal direction but from the bottom surface of the light guiding means. Therefore, Japanese Patent Laid-Open Publication No. 2005-123675 does not describe efficiently utilizing light emitted by a light source in a light guide in which light enters from an end in a longitudinal direction.